There have been demands for a television system capable of providing a high resolution. To meet such demands, a television system called the EDTV (Extended Definition Television) system was introduced and has been put to practical use. The MUSE (Multiple Sub-nyquist Sampling Encoding) system, which is one of the HDTV (High-definition Television) systems, has been proposed, and some of the MUSE systems have been put to practical use. It is expected that advanced television systems such as an EDTV II system (i.e., the second-generation EDTV) and a digital television system will come in practice in the near future. In view of these developments in the field of TV broadcasting system, video signal processors including television receivers and video tape recorders must be designed such a way that they can receive broadcasting signals of different television systems including the existing NTSC (National Television System Committee) system. A conventional TV receiver has plural different boards each of which corresponds to a respective television system. These boards are exchanged depending on the received signal. This technique is introduced as a background technique of "Scan Line Conversion LSI for Wide Screen TV Receiver", ITEJ Technical Report, vol.16, No.71, pp.19-24, BCS'92-41 (October, 1992) by Toshichika Satoh et al.
How conventional TV receivers having a MUSE signal processing board and a NTSC signal processing board operate is described. According to the MUSE system standard, the sampling rate=16.2 MHz; the number of pixels (per scanning line)=480; and the number of scanning lines=1125. On the other hand, according to the NTSC system standard, the sampling rate=14.3 MHz; the number of pixels (per scanning line)=910; and the number of scanning lines=525.
First, the MUSE signal is considered. The MUSE signal processing board separates a received MUSE signal into a Y signal, an R-Y signal, and a B-Y signal. In the MUSE system, in order to make high vision signals fall within the specified transmission bandwidth range, pixel data is band-compressed by making use of the fact that pixels of a previous field coincide with pixels of a current field in the case of an image without movement and the fact that the human eye has poor resolving power to an image with movement. Therefore, the MUSE processing board performs different processes depending upon the image type. An image without movement is processed according to a procedure that mainly consists of two processes; namely interpolation between specified frames (inter-frame interpolation) and interpolation between specified fields (inter-field interpolation). For the case of images without movement, each one-picture (frame) data is transmitted after it is divided into four fields, pixels contained in these fields are synthesized, and the result of the synthesis operation is output. On the other hand, an image with movement is processed according to a procedure that mainly consists of two processes; namely intra-field interpolation and frequency conversion. In the case of images with movement it is not possible to make use of data about a previous field. This means that desired pixels must be generated from data about a current field by an interpolation technique.
On the other hand, the NTSC signal processing board separates a received NTSC signal into a Y signal, an R-Y signal, and a B-Y signal. An NTSC signal is fed in the form of a blend of a luminance signal Y and a chrominance signal C, and thus it is necessary to perform a Y/C separation process that is the NTSC signal processing board's main function. The signal C is a signal that makes a phase-inversion for every one scanning line and for every one frame. This makes it possible to fetch only the signal Y by adding a current pixel and a pixel one scanning line ahead thereof, and it is also possible to fetch only the signal C by means of subtraction. However, there actually exists a location difference between a pixel and a pixel one scanning line ahead thereof, which prevents the Y/C separation from being performed successfully. To deal with this problem, a pixel at the same location as a current pixel is first pseudo-found from an average of vertical lines and thereafter addition/subtraction operations are performed for the Y/C separation to be performed completely. For the case of images without movement, the complete Y/C separation can be carried out by making use of a pixel one frame ahead of a current pixel.
As described above, conventional TV receivers have to contain a plurality of signal processing boards for compatibility with different types of TV broadcasting systems. This results in the increase in costs. Additionally, to catch up with new TV broadcasting systems that are expected to be put to practical use in the future, new signal processing boards corresponding to these new systems must be developed. This requires much development work, thereby increasing the development cost.
The conventional TV receiver has some problems. For example, in order to perform vertical/horizontal synchronization when outputting a picture to a CRT, it is necessary to operate the entire TV receiver at different system clock signals having different frequencies depending on the input video signal type. That is, a system clock frequency of 16.2 MHz is used in the case of the MUSE system, and 14.3 MHz in the case of the NTSC system. When aiming at achieving high-speed image processing, sampling clock processing for phase lock becomes a barrier to increasing the system clock signal frequency (i.e., the processing frequency). There may be a way capable of realizing high-speed processing without increasing the system clock signal frequency such as parallel processing. This way, however, produces the problem that the amount of hardware increases.